1. Field of the Invention
This invention is related to semiconductor switcher structures for switching an array of capacitors used in step-down or step-up DC to DC power converters. This is a four-terminal switcher with a control gate for providing switching function to connect or disconnect an array of capacitors to form series or parallel configurations.
2. Description of the Prior Art
Switching capacitor is one of the original concepts for the energy conversion. It is available in very limited application such as the energy source for high voltage discharge by connecting an array of capacitors in parallel configuration for charging and in series configuration for discharging. Mechanical switchers in manual operations are usually used for this kind of application. However, due to unavailable very low on resistance and low cost semiconductor switcher, this approach has not been realized for the electronic equipment. Most of the power suppliers and DC to DC converters available today are using transformers, inductors and capacitors for the energy conversion in conjunction with rectifiers, MOS transistors, bipolar transistors and/or integrated circuits. Marek S. Makowski et al published an article, "Performance Limits of Switched-Capacitor DC-DC Converters", P. 249, Power Electronics Technology and Applications, Edited by Dr. Fred C. Lee, IEEE TK7881.15, 1997. In this article, theoretical performance limits of switching capacitor DC-DC converter are calculated. It is clearly indicated in this article that the overall efficiency of the converter is a function of the contact resistance of the switcher. A contact resistance of 2 ohms was used in the calculation; therefore, the low efficiency of this kind of converter is resulted. No structure or description of the switcher is discussed in this article. The inventor has submitted several patent ideas to patent office: 1) "Low On Resistance Transistors and the Method of Making", Filed in Patent Office of Disclosed Document Program, Sep. 24, 1998, #444899, provisional application, 60/115,009, was filed on Jan. 6, 1999 and the utility patent application was filed on Oct. 28, 1999. This patent application disclosed low on resistance Junction Field Effect Transistor (JFET) device structures and the fabrication steps for normally "on" JFETs. 2) "Novel Structure of JFETs for Low Voltage Applications", Filed in Patent Office of Disclosed Document Program, Sep. 16, 1998, #444874. This is a normally "off" Junction Field Effect Transistors (JFETs) to provide low on resistance in "on" state. This kind of normally "off" JFET is used in current patent disclosure. The concept of this patent disclosure also filed on Jan. 6, 1999 and Oct. 28, 1999 in combine with 1) to the Patent Office.